How to Measure Aluminium Doors: A Step-by-Step Guide

Knowing how to measure aluminium doors properly is the most important step before you order. Doors need a few checks that windows do not – the floor level, the threshold, the door type and the opening direction. Coetz™ doors are made to order and supplied without installation, so the size you give us is the size we make. This guide shows you how to measure aluminium doors step by step for sliding, folding, hinged, pivot and stable doors, and how to turn your measurements into the right size to order.

What you need

• A steel tape measure of at least 5 m – a fabric tape stretches over wide door openings.
• A pencil and paper or your phone, to record every reading as you take it.
• A spirit level to check the floor and the sides of the opening.
• A helper for wide sliding, folding and stacking door openings.

Work in millimetres throughout. It is the unit our door sizes and the estimator use.

Which opening to measure

The first rule of how to measure aluminium doors: measure the opening the door frame will fit into – the brick opening on a new build, or the plastered opening if plastering is done. For a replacement, take the old frame out first if you can and measure the opening behind it. Old frames are often packed or out of square, so measuring them repeats old mistakes.

How to measure aluminium doors, step by step

This is how to measure aluminium doors for any opening, from a single back door to a wide patio. Follow the same six steps every time:

1. Measure the width in three places – near the top, in the middle and near the bottom of the opening. Use the smallest figure.
2. Measure the height in three places – on the left, in the centre and on the right – from the finished floor level up to the underside of the lintel. Use the smallest figure.
3. Allow for the floor finish. If the floor is not yet tiled or screeded, ask your builder for the finished floor level and measure from there, or the door will end up too high or too low at the threshold.
4. Check the floor is level across the width of the opening. Sliding and folding door tracks must sit level along their whole length.
5. Check the diagonals corner to corner. A difference of more than about 10 mm means the opening is out of square – tell your installer.
6. Write the size as width × height, for example 2400 × 2100, and label the opening by room.

Turn your measurements into the right size

Knowing how to measure aluminium doors is only half the job – the other half is ordering the right size. Coetz™ doors are sold in standard catalogue sizes, and the size you order is the opening size. The frame is made 10 mm smaller than the size you order, which leaves a fitting gap for packing, levelling and sealing. For example, a 2400 × 2100 door has a 2390 × 2090 frame.

• Your opening matches a standard size: order that size in the shop or the estimator.
• Your opening is between two standard sizes: use the online estimator. It prices your opening at the next standard size up and the door is made to fit your opening.
• Your opening is wider than a door type is made: choose a door with more panels, add a sidelight, or send the opening to us for a quote.
• Never order a standard size larger than your opening. It will not fit.

Wide openings need a proper lintel above them, built by your builder – the door frame is not designed to carry the wall.

Measuring by door type

How to measure aluminium doors is the same for every type, but each type needs a few extra details:

• Sliding and patio doors – measure the full opening. Note how many panels you want, which panels slide and which are fixed, and where you want the sidelights or toplights, if any. StormSeal sliding doors come with a low or a high threshold.
• Folding (bi-fold) doors – measure the full opening. The number of panels sets how wide each panel is. When open, the panels fold and stand stacked at one end of the opening, on the outside – keep that area clear of furniture, plants and burglar bars.
• Stacking doors – measure the full opening and decide which side the panels stack to.
• Hinged and French doors – measure the opening and decide whether you need a single or a double door.
• Pivot and swing doors – measure the opening; these are wide single doors for entrances.
• Stable doors – measure like a hinged door; the top and bottom leaves open separately.

Measuring special door openings

A few openings change how to measure aluminium doors a little:

• A door with a sidelight. Measure the full opening, then decide how much of the width is door and how much is fixed glass. Order the door and the sidelight as separate items, and add their widths together to check the total fits the opening.
• A door with a toplight. Measure the full height, then subtract the toplight height (toplights are 600 mm high) to get the door height you need.
• A step down to a patio or garden. Measure the height from the inside finished floor. Make sure the outside level is lower than the threshold, so rain runs away from the door rather than towards it.
• Replacing a timber door and frame. Timber frames are often thicker than aluminium frames. Take the old frame out and measure the opening behind it, otherwise you will order a door that is too small.
• Very wide patio openings. If the opening is wider than one door is made, a sliding door with more panels, a folding door or two units side by side may suit it better. The estimator shows which sizes are available.

Choosing the door type from your measurements

Your opening width usually narrows down the choice of door:

• Up to about 1 metre wide – a single hinged or stable door. Add a sidelight if the opening is a little wider.
• About 1.2 to 1.8 metres – a double hinged or French door, a pivot door, or a two-panel sliding door.
• Wider patio openings – a sliding door with three, four or six panels, or a folding door that opens almost the whole width.

Not sure which suits your opening? Our comparisons of sliding doors vs folding doors and hinged doors vs pivot doors explain the trade-offs, and the estimator shows every standard size for each door. Planning an automatic entrance instead? Automatic sliding doors are measured differently – see how to measure for an automatic sliding door.

Opening direction and handing

Knowing how to measure aluminium doors includes choosing the opening direction. Hinged, pivot and stable doors open in or out, and you choose this when you order. Decide based on the space available inside and outside, and on weather – an outward-opening door is easier to seal against driving rain.

Describe the handing as seen from inside the building, for example “hinged on the left, opening out, viewed from inside”. All our drawings are viewed from inside, so describing it the same way avoids mistakes. Sliding, folding and stacking doors do not open in or out – note which side the panels slide or stack to instead.

Common mistakes when you measure aluminium doors

Learning how to measure aluminium doors properly avoids all of these common mistakes:

• Measuring the height from a raw slab instead of the finished floor level.
• Measuring the old frame instead of the opening behind it.
• Measuring only once instead of in three places.
• Forgetting the opening direction and handing of hinged and stable doors.
• Ordering a bigger standard size than the opening.
• Ignoring a sloping floor under a sliding or folding door track.
• No clear space outside for the stacked panels of a folding door.

Measuring checklist

• Width measured at the top, middle and bottom – smallest noted
• Height measured left, centre and right from the finished floor – smallest noted
• Floor checked for level, diagonals checked for square
• Size written as width × height in millimetres
• Door type and number of panels chosen
• Opening direction and handing noted (viewed from inside), or slide and stack side for sliding and folding doors
• Colour chosen – see aluminium window and door colours
• Opening labelled by room

Price every door in one go

Once you know how to measure aluminium doors, pricing the whole project takes minutes. When all your openings are measured, the Whole project tab of the online estimator prices every window and door in one list, with delivery and VAT. You can pay online, send the list to us, or download a PDF price schedule. Our window price calculator guide explains each step.

Who measures – and who installs

Coetz™ aluminium windows and doors are supply only: we do not do site visits, and you or your builder take the measurements. If you are unsure, WhatsApp your figures and a photo to 076 613 4418 and we will check them against the standard sizes before you order. Final responsibility for the measurements stays with the customer, as set out in our terms and conditions.

Your installer may know how to measure aluminium doors and measure for you – see our guide to finding aluminium window installers. Doors are heavy, so large sliding and folding doors need two or more people to install.

When your doors arrive

Knowing how to measure aluminium doors also helps when they arrive: check every door against your order on delivery or collection – size, colour, glass and opening direction – and report damage or mistakes within 48 hours, before installation. See our delivery and returns and refunds pages. All doors are glazed with 6.38 mm clear laminated safety glass, in line with the National Building Regulations (SANS 10400 Part N), except our Patio sliding doors and a few large Elite sliding door sizes, which use toughened safety glass.

Measuring windows too? See how to measure aluminium windows.

Once you have the opening size, choose a layout with our guide to sliding door configurations, and add toplights and sidelights if the opening is taller or wider than the door.

Once the doors arrive, follow our guide on how to install aluminium windows and doors.

Frequently asked questions

Do I measure the height from the slab or the finished floor?

From the finished floor level. If the floor is not finished yet, get the finished floor level from your builder and measure from there, otherwise the door will sit too high or too low.

Do I need to subtract anything for a fitting gap?

No. When you work out how to measure aluminium doors for an order, simply use the opening size. The frame is made 10 mm smaller than the size you order, which leaves the fitting gap.

What if my opening is between two standard sizes?

Use the online estimator. It prices your opening at the next standard size up and the door is made to fit your opening. Never order a standard size larger than your opening.

How do I describe which way my door opens?

Say whether it opens in or out, and which side the hinges are on, as seen from inside – for example “hinged on the left, opening out, viewed from inside”.

Will Coetz come and measure my doors?

No. Aluminium doors are supply only, so we do not do site visits. You or your builder measure, and we are happy to check your figures on WhatsApp before you order.

Is it different to measure aluminium doors for a replacement?

The method is the same, but take the old frame out first if you can. Knowing how to measure aluminium doors for a replacement mostly comes down to measuring the opening behind the old frame and checking the floor level, because old thresholds are often built up.

Can I return a door if I measured wrongly?

No. Doors are made to the size you order, so a measuring mistake is not grounds for a return. Measure twice and check your sizes before ordering.

Standard sizes: see aluminium sliding door sizes.

Standard sizes: see aluminium door sizes.